The present invention relates to a linear pretensioning drive for tightening a vehicle seat belt.
A pretensioning drive taught in taught in EP 1 060 958 A1 has a guide tube with a drivable piston, which is connected to a seat belt via a pulling means, for instance a traction cable. The traction cable is connected to a belt buckle of the seat belt. When driven, for instance with the help of a pyrotechnic driving means, the piston is guided along the guide tube. To avoid a return stroke of the piston in the opposite direction to the drive direction after the pretensioning of the seat belt, a reverse movement lock is provided on the piston in the form of a ball ring. The reverse movement lock is in this case moved into a locking position, by which the return stroke of the piston in the opposite direction to the drive direction is avoided. If the reverse movement lock is formed by a ball ring, the balls of which are arranged around the longitudinal axis of the guide tube, the individual balls lie against merely a small supporting surface of the inner wall of the guide tube in the locking position. Due to these small surface contact points lying on a circle, an excessive load can be exerted on the guide tube. This load can also occur when clamping bodies are used with line-shaped or small supporting surfaces.
There is provided in accordance with the present invention a linear pretensioning drive for tightening a vehicle seat belt comprising: a guide tube; a piston that is located inside the guide tube and can be driven along a longitudinal axis of the guide tube in a drive direction; and a reverse movement lock comprising locking elements arranged on a ring around the longitudinal axis of the guide tube, the locking elements, on movement of the piston in an opposite direction to the drive direction, assume a locking position between the piston and the guide tube, which locks the further return stroke of the piston against the drive direction, in the drive direction in front of the reverse movement lock at least one support part is provided which, in the locking position, lies against an inner wall of the guide tube with a greater supporting surface than each locking element of the reverse movement lock.